Systems for forming a ceramic matrix composite structure, and related advanced fiber placement apparatuses

ABSTRACT

A method of forming a ceramic matrix composite structure. The method comprises forming at least one prepregged composite material comprising a ceramic fiber preform and a pre-ceramic matrix slurry. The at least one prepregged composite material is placed over at least one surface of a tool using an advanced fiber placement apparatus to form an at least partially uncured composite material structure. The at least partially uncured composite material structure is exposed at least to elevated temperatures to convert the at least partially uncured composite material structure into a ceramic matrix composite structure. A system for forming a ceramic matrix composite structure, an advanced fiber placement apparatus, and a ceramic matrix composite structure are also described.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/741,052, filed Jan. 14, 2013, pending, the disclosure of which ishereby incorporated herein in its entirety by this reference.

FIELD

The disclosure, in various embodiments, relates generally to methods offorming ceramic matrix composite structures, and to related systems,apparatuses, and ceramic matrix composite structures. More specifically,the disclosure relates to methods of forming ceramic matrix compositestructures using an advanced fiber placement apparatus, and to relatedsystems, apparatuses, and ceramic matrix composite structures.

BACKGROUND

A ceramic matrix composite (CMC) is a material including reinforcingceramic fibers embedded in a ceramic matrix. CMCs can exhibit a varietyof desirable properties, such as high temperature stability, highthermal resistance, high mechanical integrity, high hardness, highcorrosion resistance, light weight, nonmagnetic properties, andnonconductive properties. CMCs can thus be used to form a number ofindustrial and military structures including, for example, aerospace,marine, and automotive structures requiring one or more of theaforementioned properties.

One approach toward forming CMC structures includes the use of resintransfer molding (RTM). To form a CMC structure using RTM, ceramicfibers are placed into a mold in a desired arrangement. The mold is thenevacuated, a resin is introduced into the mold under pressure, and thetemperature of the mold is controlled to enable the resin to set. Theresin is then cured and pyrolyzed at elevated temperatures to form theCMC structure. Unfortunately, however, RTM is generally limited to usein forming relatively small CMC structures (e.g., due to mold sizelimitations), and can result in ceramic matrix uniformity issues. Forexample, gas bubbles can be introduced into or evolve within the resinduring processing that cannot escape or are difficult to remove duringcure and pyrolysis. Consequently, the gas bubbles may be present in theceramic matrix of the CMC structure, and can negatively affect thedesired properties thereof.

Another approach toward forming CMC structures includes the use ofchemical vapor infiltration (CVI). To form a CMC structure using CVI,dry ceramic fiber preforms, such as dry ceramic woven fabrics, areplaced on a tool in a desired arrangement to form a dry ceramic fiberstructure. A chemical vapor deposition (CVD) process is then used toinfiltrate the dry ceramic fiber structure with a ceramic matrix andform the CMC structure. Unfortunately, however, CVI requires complex andcostly tooling to ensure that the dry ceramic fiber structure isappropriately shaped, and to ensure the CMC structure includes a uniformceramic matrix. In addition, the nature of the CVD process typicallylimits the reusability of the tooling, significantly adding to CMCstructure fabrication costs.

Yet another approach toward forming CMC structures involves handplacement (e.g., lay up) of ceramic fiber preforms, such as ceramictapes or ceramic woven fabrics, infiltrated with a pre-ceramic matrixslurry onto a tool to form an uncured composite material structure. Theuncured composite material structure is then cured and either sinteredor pyrolyzed to form a desired CMC structure. Unfortunately, however,such processing can be prohibitively expensive as hand placement can betime and labor intensive, as well as enhancing potential for productdefects due to human error.

Yet still another approach toward forming CMC structures involvesfilament winding of ceramic fiber tows infiltrated with a pre-ceramicmatrix slurry onto a tool to form an uncured composite materialstructure. The uncured composite material structure is then cured andeither sintered or pyrolyzed to form a desired CMC structure.Unfortunately, however, filament winding is generally limited to formingCMC structures that are substantially cylindrical in shape. Namely, thetool upon which the tows are wound is generally limited to beingsubstantially cylindrical in shape so that the tows follow a placementpath permitting the tows to remain in place on the tool (i.e., ageodesic path).

It would, therefore, be desirable to have new methods, systems, andapparatuses for forming a CMC structure that are easy to employ,cost-effective, fast, and more versatile as compared to conventionalmethods, systems, and apparatuses for forming CMC structures. Suchmethods, systems, and apparatuses may, for example, facilitate increasedadoption and use of CMC structures in industrial and militaryapplications.

SUMMARY

Embodiments described herein include methods of forming ceramic matrixcomposite structures, and related systems, apparatuses, and ceramicmatrix composite structures. For example, in accordance with oneembodiment described herein, a method of forming a ceramic matrixcomposite structure comprises forming at least one prepregged compositematerial comprising a ceramic fiber preform and a pre-ceramic matrixslurry. The at least one prepregged composite material is placed over atleast one surface of a tool using an advanced fiber placement apparatusto form an at least partially uncured composite material structure. Theat least partially uncured composite material structure is exposed atleast to elevated temperatures to convert the at least partially uncuredcomposite material structure into a ceramic matrix composite structure.

In additional embodiments, a system for forming a ceramic matrixcomposite structure comprises an advanced fiber placement apparatus, acuring apparatus, and a densification apparatus. The advanced fiberplacement apparatus is configured to place at least one prepreggedcomposite material over at least one surface of a tool, the at least oneprepregged composite material comprising a ceramic fiber preforminfiltrated with a pre-ceramic matrix slurry. The curing apparatus isconfigured to cure the at least partially uncured composite materialstructure to form a substantially cured composite material structure.The densification apparatus is configured to densify the substantiallycured composite material structure to form a ceramic matrix compositestructure.

In yet additional embodiments, an advanced fiber placement apparatuscomprises at least one placement head configured to draw, align, place,cut, and rethread at least one prepregged composite material comprisinga ceramic fiber preform infiltrated with a pre-ceramic matrix slurry,and at least one reel of the at least one prepregged composite material.

In yet still additional embodiments, a ceramic matrix compositestructure comprises a structure formed by the method comprising formingat least one prepregged composite material comprising a ceramic fiberpreform and a pre-ceramic matrix slurry, placing the at least oneprepregged composite material over at least one surface of a tool usingan advanced fiber placement apparatus to form an at least partiallyuncured composite material structure, and exposing the at leastpartially uncured composite material structure at least to elevatedtemperatures to convert the at least partially uncured compositematerial structure into a ceramic matrix composite structure.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a simplified flow diagram of a method of forming a CMCstructure, in accordance with embodiments of the disclosure;

FIG. 2 is a simplified perspective view of a lay up process for themethod illustrated in FIG. 1, in accordance with embodiments of thedisclosure;

FIG. 3A is a photograph showing a top down view of a portion of aceramic fiber preform prior to being infiltrated with a pre-ceramicmatrix slurry, as described in the EXAMPLE provided herein;

FIG. 3B is a side-elevation view illustrating a placement head of an AFPapparatus used to place a prepregged composite material on a surface ofa tool, as described in the EXAMPLE provided herein;

FIG. 3C is a photograph showing a side-elevation view of two layers of aprepregged composite material on a tool, as described in the EXAMPLEprovided herein;

FIG. 3D is a photograph showing a perspective view of a cured compositematerial structure, as described in the EXAMPLE provided herein; and

FIG. 3E is a photograph showing a perspective view of a CMC structure,as described in the EXAMPLE provided herein.

DETAILED DESCRIPTION

Methods of forming a CMC structure are described, as are relatedsystems, apparatuses, and CMC structures. In some embodiments, a methodof forming a CMC structure includes placing (e.g., “laying up”) aprepregged composite material on or over at least one surface of a toolusing an advanced fiber placement (AFP) apparatus (which may also bereferred to as an “automated” fiber placed apparatus) to form an atleast partially uncured composite material structure. The at leastpartially uncured composite material structure may then be cured andeither sintered or pyrolyzed to form the CMC structure. The CMCstructure may exhibit properties desirable for use in a wide variety ofindustrial and military applications. The methods, systems, andapparatuses of embodiments of the disclosure may be faster, morecost-efficient, and more versatile than conventional methods, systems,and apparatuses used to form CMC structures.

The following description provides specific details, such as materialtypes and processing conditions in order to provide a thoroughdescription of embodiments of the disclosure. However, a person ofordinary skill in the art would understand that the embodiments of thedisclosure may be practiced without employing these specific details.Indeed, the embodiments of the disclosure may be practiced inconjunction with conventional techniques employed in the industry. Onlythose process acts and structures necessary to understand theembodiments of the disclosure are described in detail below. Additionalacts to form a CMC structure of the disclosure may be performed byconventional techniques, which are not described in detail herein. Also,the drawings accompanying the application are for illustrative purposesonly, and are thus not drawn to scale. In addition, elements commonbetween figures may retain the same numerical designation.

As used herein, the terms “comprising,” “including,” “containing,”“characterized by,” and grammatical equivalents thereof are inclusive oropen-ended terms that do not exclude additional, unrecited elements ormethod steps, but also include the more restrictive terms “consistingof” and “consisting essentially of” and grammatical equivalents thereof.As used herein, the term “may” with respect to a material, structure,feature or method act indicates that such is contemplated for use inimplementation of an embodiment of the disclosure and such term is usedin preference to the more restrictive term “is” so as to avoid anyimplication that other, compatible materials, structures, features andmethods usable in combination therewith should or must be, excluded.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

As used herein, relational terms, such as “first,” “second,” “over,”“top,” “bottom,” “underlying,” etc., are used for clarity andconvenience in understanding the disclosure and accompanying drawingsand does not connote or depend on any specific preference, orientation,or order, except where the context clearly indicates otherwise.

As used herein, the term “substantially,” in reference to a givenparameter, property, or condition, means to a degree that one ofordinary skill in the art would understand that the given parameter,property, or condition is met with a small degree of variance, such aswithin acceptable manufacturing tolerances.

FIG. 1 is a simplified flow diagram illustrating a method of forming aCMC structure in accordance with embodiments of the disclosure. Themethod may include a lay up process 102 including placing at least oneprepregged composite material on or over a surface of a tool using anAFP apparatus, a curing process 104 including curing the prepreggedcomposite material after placement on or over the surface of the tool toform a cured composite material structure, a densification process 106including sintering or pyrolyzing the cured composite material structureto form the CMC structure, and, optionally, a finalization process 108including further treating (e.g., machining, coating, etc.) the CMCstructure. With the description as provided below, it will be readilyapparent to one of ordinary skill in the art that the method describedherein may be used in various applications. In other words, the methodmay be used whenever it is desired to form a CMC structure.

One embodiment of the disclosure will now be described with reference toFIG. 2, which illustrates a simplified perspective view of the lay upprocess 102. As shown in FIG. 2, the lay up process 102 includes placingat least one prepregged composite material 202 on or over at least onesurface 206 of a tool 204 using an AFP apparatus 200. The prepreggedcomposite material 202 includes a ceramic fiber preform infiltrated(e.g., impregnated) with a pre-ceramic matrix slurry. As used herein,the term “ceramic fiber preform” means and includes a structure formedof and including ceramic fibers. The ceramic fibers may be continuous,and may be oriented in a direction generally parallel to, generallyperpendicular to, or at another angle with respect to a length of theceramic fiber preform. The ceramic fiber preform may comprise a singletow of the ceramic fibers (e.g., a substantially unidirectional bundleof the ceramic fibers), may comprise a tape of multiple tows of theceramic fibers (e.g., an array of substantially unidirectional tows ofthe ceramic fibers stitched together using another material, such as aglass material), or may comprise a woven fabric of multiple tows of theceramic fibers (e.g., a plain weave of the multiple tows, a 4 harnesssatin weave of the multiple tows, a 5 harness satin weave of themultiple tows, an 8 harness satin weave of the multiple tows, etc.). Theceramic fiber preform may have any dimensions (e.g., length, width,thickness) compatible with the AFP apparatus 200 employed to apply theprepregged composite matrix material 202 to tool 204. For example, theceramic fiber preform may have a length enabling a desired amount of theprepregged composite material 202 to be placed on or over the surface206 of the tool 204, and may have a width compatible with a placementmeans (e.g., a placement head) of the AFP apparatus 200, such as a widthwithin a range of from about one-eighth inch to about one inch. In someembodiments, the width of the ceramic fiber preform is about one inch.

The ceramic fibers of the ceramic fiber preform may be formed of andinclude a ceramic material compatible with the other components (e.g.,the pre-ceramic matrix slurry) of the prepregged composite material 202,of appropriate physical characteristics for reinforcing the CMCstructure to be formed, and formulated to withstand the processingconditions (e.g., temperatures, pressures, ambient atmosphere, etc.)used to form the CMC structure. As used herein, the term “compatible”means and includes a material that does not react with, break down, orabsorb another material in an unintended way, and that also does notimpair the chemical and/or mechanical properties of the another materialin an unintended way. The ceramic fibers may be oxide ceramic fibers, ormay be non-oxide ceramic fibers. The ceramic fiber preform may thus bean oxide-based ceramic fiber preform, or may be a non-oxide-basedceramic fiber preform. Non-limiting examples of suitable oxide ceramicfibers include alumina fibers, alumina-silica fibers, andalumina-boria-silica fibers. Such oxide ceramic fibers are commerciallyavailable from numerous sources including, but not limited to, 3MCompany (St. Paul, Minn.) (e.g., under the NEXTEL® 312, NEXTEL® 440,NEXTEL® 550, NEXTEL® 610, and NEXTEL® 720 tradenames). Non-limitingexamples of suitable non-oxide ceramic fibers include silicon carbidefibers, silicon nitride fibers, fibers including silicon carbide on acarbon core, silicon carbide fibers containing titanium, siliconoxycarbide fibers, silicon oxycarbonitride fibers, and carbon fibers.Such non-oxide ceramic fibers are commercially available from numeroussources including, but not limited to, COI Ceramics, Inc. (San Diego,Calif.) (e.g., under the SYLRAMIC® tradename), Nippon Carbon Co., Ltd.(Tokyo, JP) (e.g., under the CG NICALCON™, HI-NICALCON™, and NICALCONTYPE S™ tradenames), and Ube Industries (Tokyo, JP) (e.g., under theTYRANNO SA, and TYRANNO LoxM tradenames). In some embodiments, theceramic fibers of the ceramic fiber preform are NEXTEL® 610 fibers. Theceramic fiber preform including the ceramic fibers may be formed usingconventional processes and equipment, which are not described in detailherein.

The pre-ceramic matrix slurry may be a slurry suitable for forming aceramic matrix over and around the ceramic fiber preform, and includingsufficient chemical and mechanical properties (e.g., rigidity,tackiness, environmental resistance, etc.) to facilitate placement ofthe prepregged composite material 202 on or over the surface 206 of thetool 204 using the AFP apparatus 200, as described in further detailbelow. For example, the pre-ceramic matrix slurry may be a slurryformulated to enable forming an oxide ceramic matrix or a non-oxideceramic matrix upon further processing (e.g., sintering, pyrolysis,etc.), to enable the prepregged composite material 202 to be cut by theAFP apparatus 200 and to adhere at least to the surface 206 of the tool204 and to the prepregged composite material 202 itself duringplacement, and to withstand and accommodate without substantialdegradation the physical and environmental processing conditionsassociated with the placement of the prepregged composite material 202for as long as is needed to complete such placement.

As a non-limiting example, the pre-ceramic matrix slurry may be anoxide-based pre-ceramic matrix slurry including an oxide ceramic sol andan oxide ceramic filler. The oxide ceramic sol may be an alumina sol(e.g., colloidal alumina in water), a silica sol (e.g., colloidal silicain water), an alumina-silica sol (e.g., colloidal alumina-silica inwater), or a combination thereof. In some embodiments, the oxide ceramicsol is a silica sol. Solids (e.g., silica) may constitute from about 15percent to about 60 percent of the total weight of the oxide ceramicsol. In turn, the oxide ceramic filler may include particles of at leastone oxide ceramic material, such as particles of at least one ofalumina, silica, zirconia. In some embodiments, the oxide ceramic fillerincludes particles of alumina. Each of the particles may be of a desiredsize (e.g., within a range of from about 20 nanometers to about 1000nanometers) and shape (e.g., a spherical shape, a hexahedral shape, anellipsoidal shape, a cylindrical shape, an irregular shape, etc.). Inaddition, the particles may be monodisperse, wherein each of theparticles has substantially the same size and shape, or may bepolydisperse, wherein the particles include a variety of sizes and/orshapes.

The ratio of the oxide ceramic sol to the oxide ceramic filler in theoxide-based pre-ceramic matrix slurry may depend on the properties(e.g., thermal stability, viscosity, weight, conductivity, etc.) of thematerials selected for the oxide ceramic sol and the oxide ceramicfiller, on the processing conditions used to form the CMC structure fromthe prepregged composite material 202, and on the desired properties(e.g., thermal stability, thermal-shock resistance, mechanicalstability, hardness, corrosion resistance, weight, conductivity, etc.)of the CMC structure to be formed. The oxide-based pre-ceramic matrixslurry may, for example, include from about 20 percent by weight toabout 60 percent by weight of the oxide ceramic sol, such as from about25 percent by weight to about 40 percent by weight, and may include fromabout 20 percent by weight to about 80 percent by weight of the oxideceramic filler, such as from about 40 percent by weight to about 70percent by weight. In some embodiments, the oxide-based pre-ceramicmatrix slurry includes about 28 percent by weight silica sol, and about60 percent by weight alumina filler.

Optionally, the oxide-based pre-ceramic matrix may also include at leastone processing aid. The processing aid may comprise a material that,when combined with the processing conditions (e.g., temperatures,pressures, ambient environment, etc.) applied before, during, and afterplacement of the prepregged composite material 202, enhances one or moreproperties of the prepregged composite material 202. The processing aidmay, for example, comprise a material that enhances at least one of therigidity, tackiness, and environmental resistance properties (e.g.,maximum possible exposure time to processing conditions) of theprepregged composite material 202 before and during placement of theprepregged composite material 202 on the surface 206 of the tool 204.For example, the processing aid may comprise a water-soluble organicmaterial including, but not limited to, a polyol (e.g., glycerol), acellulose gum (e.g., methyl cellulose), a vinyl alcohol (e.g., polyvinylalcohol), a glycol (e.g., propylene glycol, ethylene glycol), and acaciagum. In some embodiments, the at least one processing aid includespropylene glycol and polyvinyl alcohol. If included, the processing aidmay constitute from about 0.1 percent to about 20 percent of the totalweight of the oxide-based pre-ceramic matrix, such as from about 5percent to about 15 percent of the total weight of the oxide-basedpre-ceramic matrix. In some embodiments, the oxide-based pre-ceramicmatrix includes about 10.5 percent by weight propylene glycol, and about1.5 percent by weight polyvinyl alcohol.

As another non-limiting example, the pre-ceramic matrix slurry may be anon-oxide-based pre-ceramic matrix slurry including a non-oxidepre-ceramic polymer, and a non-oxide ceramic filler. The non-oxidepre-ceramic polymer may be an organosilicon polymer formulated to form anon-oxide ceramic matrix upon further processing (e.g., curing andpyrolysis), and having sufficient chemical and mechanical properties tofacilitate placement of the prepregged composite material 202. Forexample, the non-oxide pre-ceramic polymer may comprise at least one ofa polysiloxane, a polysilazane (e.g., at least one of ahydridopolysilazane, a silacyclobutasilazane, a boron modifiedhydridopolysilazane, and a vinyl-modified hydridopolysilazane), apolysilane, a polycarbosilane, a polycarbosilazane, and apolysilsesequioxane, that enables the prepregged composite material 202to be cut by the AFP apparatus 200 and to be placed on or over thesurface 206 of the tool 204 using the AFP apparatus 200. Suitablenon-oxide pre-ceramic polymers are commercially available from numeroussources including, but not limited to, Starfire Systems (Schenectady,N.Y.) (e.g., under the SMP-500, and SMP-800 tradenames). In someembodiments, the non-oxide pre-ceramic polymer is SMP-500. In turn, thenon-oxide ceramic filler may include particles of at least one non-oxideceramic material, such as particles of at least one of silicon carbide,silicon nitride, silicon hexaboride, aluminum nitride, boron nitride,boron carbide, titanium boride, titanium carbide, and hafnium carbide.In some embodiments, the non-oxide ceramic filler material includesparticles of silicon carbide. Each of the particles may be of a desiredsize (e.g., within a range of from about 20 nanometers to about 1000nanometers) and shape (e.g., a spherical shape, a hexahedral shape, anellipsoidal shape, a cylindrical shape, an irregular shape, etc.). Inaddition, the particles may be monodisperse, wherein each of theparticles has substantially the same size and shape, or may bepolydisperse, wherein the particles include a variety of sizes and/orshapes.

The ratio of the non-oxide pre-ceramic polymer to the non-oxide ceramicfiller in the non-oxide-based pre-ceramic matrix slurry may be relatedto the properties (e.g., thermal stability, viscosity, weight,conductivity, etc.) of the materials selected for the non-oxidepre-ceramic polymer and the non-oxide ceramic filler, on the processingconditions used to form the CMC structure from the prepregged compositematerial 202, and on the desired properties (e.g., thermal stability,thermal-shock resistance, mechanical stability, hardness, corrosionresistance, weight, conductivity, etc.) of the CMC structure to beformed. The non-oxide-based pre-ceramic matrix slurry may, for example,include from about 20 percent by weight to about 60 percent by weight ofthe non-oxide pre-ceramic polymer, such as from about 30 percent byweight to about 50 percent by weight, and may include from about 20percent by weight to about 60 percent by weight of the non-oxide ceramicfiller, such as from about 30 percent by weight to about 50 percent byweight.

Optionally, the non-oxide pre-ceramic matrix may also include one ormore of at least one curing catalyst, and at least one compatiblesolvent (e.g., tetrahydrofuran, hexane, heptane, benzene, toluene,xylene, etc.). As used herein, the term “curing catalyst” refers to amaterial capable of substantially catalyzing the deep sectioninfusibilization (e.g., cure) of the non-oxide pre-ceramic polymer inthe prepregged composite material 202. Suitable curing catalysts arecommercially available from numerous sources including, but not limitedto, Sigma-Aldrich (St. Louis, Mo.) (e.g., under the LUPEROX® 101tradename). If included, the curing catalyst may constitute from about0.1 percent to about 2 percent of the total weight of the oxide-basedpre-ceramic matrix, such as from about 0.1 percent to about 1.5 percentof the total weight of the oxide-based pre-ceramic matrix.

The prepregged composite material 202 including the ceramic fiberpreform and the pre-ceramic matrix slurry may be formed usingconventional processes and equipment, which are not described in detailherein. By way of non-limiting example, the pre-ceramic matrix slurrymay be formed over and around the ceramic fibers of the ceramic fiberpreform using at least one of a conventional spray-coating process, aconventional immersion-coating process, and a conventional soakingprocess. Regardless of the process utilized to form the prepreggedcomposite material 202, the process may be controlled to facilitate auniform and complete infiltration of the pre-ceramic matrix slurry overand around the ceramic fiber preform.

In some embodiments, such as where it is desired to form a CMC structureincluding an non-oxide ceramic matrix over and around the ceramic fiberpreform, at least one interfacial material may be formed on the ceramicfiber preform prior to forming the pre-ceramic matrix slurry over andaround the ceramic fiber preform. The interfacial material may, forexample, be a material facilitating or enhancing interfacial bondingbetween the ceramic fiber preform and the pre-ceramic matrix slurry. Byway of non-limiting example, the interfacial material may be at leastone of boron nitride, silicon nitride, silicon carbide, aluminumnitride, boron carbide, and carbon. The interfacial material may beformed on or over the ceramic fiber preform using conventional processes(e.g., chemical vapor deposition, coating with polymer precursorsfollowed by pyrolysis, etc.) and equipment, which are not described indetail herein.

With continued reference to FIG. 2, the tool 204 may be a structureexhibiting a desired configuration (e.g., size, and shape), that ischemically and mechanically compatible with the prepregged compositematerial 202, and that is capable of withstanding the processingconditions (e.g., temperatures, pressures, ambient environment, etc.)used to place the prepregged composite material 202 on or over thesurface 206 thereof using the AFP apparatus 200. The tool 204 may, forexample, have a three-dimensional shape, such as a conical shape, apyramidal shape, a cubic shape, a cuboidal shape, a spherical shape, ahemispherical shape, a cylindrical shape, a semicylindrical shape,truncated versions thereof, or an irregular shape. Irregularthree-dimensional shapes include complex shapes, such as shapesassociated with aerospace, marine, and automotive structures and devices(e.g., hot exhaust structures, such as exhaust ducts, nozzles, fancowls, and thrust reversers; auxiliary power units; fuselages; taperedwing skins; nose cones; etc.). The surface 206 of the tool 204 may thusbe planar or non-planar (e.g., contoured, such as at least partiallyconcave, at least partially convex, or a combination thereof). The tool204 may be formed using conventional processes and equipment, which arenot described in detail herein.

The tool 204 may be stationary, or may be mobile. For example, asdepicted in FIG. 2, the tool 204 may be removably attached to a rotationdevice 208 configured for rotating the tool 204 during placement of theprepregged composite material 202 thereon or thereover. If performed,rotation of the tool 204 may be controlled (e.g., by way of computernumerical control) relative to the AFP apparatus 200 so that theprepregged composite material 202 is placed on or over the surface 206of the tool 204 in a desired configuration (e.g., pattern).

The AFP apparatus 200 may be any AFP apparatus configured and operatedto place the prepregged composite material 202 on or over the surface206 of the tool 204. For example, the AFP apparatus 200 may be aconventional multi-axis AFP apparatus configured and operated to draw,align, place, cut, and rethread the prepregged composite material 202.As shown in FIG. 2, the AFP apparatus 200 may, for example, include aplacement head 212 configured and operated to draw the at least oneprepregged composite material 202 (e.g., in the form of one or moreceramic tow(s), ceramic tape(s), or ceramic woven fabric(s) infiltratedwith the pre-ceramic matrix slurry) from at least one reel 210, to alignand place at least a portion the prepregged composite material 202 on orover the surface 206 of the tool 204, to cut the prepregged compositematerial 202 following placement, and to rethread the prepreggedcomposite material 202 for additional placement as desired. The AFPapparatus 200 may also be configured and operated to manipulate one ormore physical properties (e.g., tackiness, rigidity, etc.) of theprepregged composite material 202 before and/or during placement on orover the surface 206 of the tool 204. For example, the AFP apparatus 200may be configured and operated to cool the prepregged composite material202 (e.g., to increase the rigidity thereof) to a temperature within arange of from about −25° C. to about 35° C. prior to placement on orover the surface 206 of the tool 204, and/or to heat the prepreggedcomposite material 202 (e.g., to increase the tackiness thereof) to atemperature within a range of from about 85° C. to about 165° C. duringplacement on or over the surface 206 of the tool 204. Manipulation ofthe physical properties of the prepregged composite material 202 mayoccur in a single portion of the AFP apparatus 200 (e.g., within theplacement head 212), or may occur in multiple portions of the AFPapparatus 200 (e.g., within an enclosure containing the at least onereel 210, and within the placement head 212). Operations performed bythe AFP apparatus 200 may be substantially automatic (e.g., through useof computer numerical control). Non-limiting examples of AFP apparatusessuitable for use as the AFP apparatus 200 are described in U.S. Pat.Nos. 5,290,389, 6,050,315, and 6,096,164, the entire disclosure of eachof which is incorporated in its entirety herein by reference.

The AFP apparatus 200 may place multiple prepregged composite materials202 (e.g., multiple ceramic tows, ceramic tapes, and/or ceramic wovenfabrics infiltrated with the pre-ceramic matrix slurry) in continuous,edge to edge, contact, on the surface 206 of the tool 204. The multipleprepregged composite materials 202 may be placed simultaneously,sequentially, or a combination thereof. In addition, the AFP apparatus200 may place additional prepregged composite materials 202 (e.g.,additional ceramic tows, ceramic tapes, and/or ceramic woven fabricsinfiltrated with the pre-ceramic matrix slurry) on or over the multipleprepregged composite materials 202 previously placed using the AFPapparatus 200. Accordingly, the AFP apparatus 200 may place theprepregged composite materials 202 on the surface 206 of the tool 204 toany desired amount of coverage and to any desired thickness. Themultiple prepregged composite materials 202 may form an at leastpartially uncured composite material structure (not shown) on or overthe surface 206 of the tool 204. In addition, if multiple layers (e.g.,plies) of the prepregged composite materials 202 are placed over thesurface 206 of the tool 204, each layer of the prepregged compositematerials 202 may extend in substantially the same direction (e.g., eachceramic tow, ceramic tape, and/or ceramic woven fabric infiltrated withthe pre-ceramic matrix slurry may be oriented parallel to each otherceramic tow, ceramic tape, and/or ceramic woven fabric infiltrated withthe pre-ceramic matrix slurry), or at least one layer of the prepreggedcomposite material 202 may extend in a direction different than at leastone other layer of the prepregged composite material 202 (e.g., ceramictows, ceramic tapes, and/or ceramic woven fabrics infiltrated with thepre-ceramic matrix slurry in one layer may be oriented in a differentdirection than other ceramic tows, ceramic tapes, and/or ceramic wovenfabrics infiltrated with the pre-ceramic matrix in another layer).

The lay up process 102 (FIG. 1) has the advantage of being able toutilize AFP apparatuses that have been utilized in conventional polymermatrix composite (PMC) manufacturing. While such AFP apparatuses havebeen successfully used to fabricate PMC structures, previousutilizations of such AFP apparatuses did not recognize or appreciate thepotential for use thereof to form CMC structures.

Following the lay up process 102, the at least partially uncuredcomposite material structure may be subjected at least to the curingprocess 104 (FIG. 1) and the densification process 106 (FIG. 1) to forma CMC structure exhibiting a desired configuration. The curing process104 may include subjecting the at least partially uncured compositematerial structure to at least one of elevated temperature(s) andelevated pressure(s) (e.g., using a curing apparatus, such as aautoclave, a compression mold, or a lamination press) for a sufficientperiod of time to form a substantially cured composite materialstructure (not shown) having sufficient mechanical integrity to behandled. As a non-limiting example, if the at least partially uncuredcomposite material structure is substantially uncured, the curingprocess 104 may include placing the tool 204 including the at leastpartially uncured composite material structure formed thereon orthereover into a vacuum bag, and exposing the at least partially uncuredcomposite material structure to at least one temperature less than orequal to about 175° C. and at least one pressure less than or equal toabout 100 pounds per square inch (psi) for a sufficient period of timeto form the substantially cured composite material structure. Thesubstantially cured composite material structure may then be removedfrom the tool 204 and subjected to further processing to form the CMCstructure, as described in more detail below. Alternatively, if the atleast partially uncured composite material structure exhibits sufficientmechanical integrity, the curing process 104 may include removing the atleast partially uncured composite material structure from the tool 204,placing the at least partially uncured composite material structure onanother tool (not shown) configured to hold the at least partiallyuncured composite material, vacuum bagging the at least partiallyuncured composite material structure and the another tool, and exposingthe at least partially uncured composite material structure to theaforementioned temperature and pressure for a sufficient period of timeto form the substantially cured composite material structure.

The densification process 106 may include sintering or pyrolyzing thesubstantially cured composite material structure at elevatedtemperature(s) (e.g., using a densification apparatus, such as ahigh-temperature furnace) to form a CMC structure (not shown). Forexample, if the substantially cured composite material structureincludes an oxide pre-ceramic matrix, the substantially cured compositematerial structure may be sintered at a temperature within a range offrom about 1000° C. to about 1350° C. for a sufficient amount of time toform an oxide CMC structure exhibiting a desired amount of porosity,such as from about 10 percent porosity to about 25 percent porosity. Asanother example, if the substantially cured composite material structureincludes a non-oxide pre-ceramic matrix, the substantially curedcomposite material structure may be pyrolyzed at a temperature within arange of from about 600° C. to about 1400° C. in an inert ambientatmosphere (e.g., a nitrogen atmosphere, an argon atmosphere, etc.) toconvert at least 70 percent of the pre-ceramic polymer of the non-oxidepre-ceramic matrix to a non-oxide ceramic material and form a non-oxideCMC structure. If the pyrolysis process converts less than all of thepre-ceramic polymer to the non-oxide ceramic material, the non-oxide CMCstructure may be infiltrated with additional pre-ceramic polymer usingconventional processes, and may then be subjected to at least oneadditional pyrolysis process until the non-oxide CMC structure exhibitsa non-oxide ceramic matrix formed of and including a desired amount ofthe non-oxide ceramic material, such as a non-oxide ceramic matrixformed of and including greater than or equal to about 95 percent of thenon-oxide ceramic material.

As previously discussed with respect to FIG. 1, following thedensification process 106, the CMC structure may, optionally, besubjected to at least one finalization process 108. The finalizationprocess 108 may, for example, include one or more of machining (e.g.,trimming, planarizing, etc.), and seal coating (e.g., if the CMCstructure is a non-oxide CMC structure) the CMC structure.Alternatively, the finalization process 108 may be omitted, and the CMCstructure may be used as is.

Using the methods, systems, and apparatuses of the disclosure, theformation of CMC structures of a wide variety of shapes and sizes (e.g.,including large, complex shapes associated with military and industrialapplications) can be achieved quickly and in a cost-effective manner.Accordingly, the methods, systems, and apparatuses of the disclosure mayimprove the affordability of CMC structures, facilitating increasedproduction of aerospace, marine, and automotive structures exhibitingimproved properties (e.g., temperature stability, thermal resistance,hardness, corrosion resistance, weight, nonmagnetic properties,nonconductive properties, etc.) as compared to corresponding aerospace,marine, and automotive structures formed of non-CMC materials.

The following example serves to explain some embodiments of thedisclosure in more detail. The example is not to be construed as beingexhaustive or exclusive as to the scope of the disclosure.

Example

A pre-ceramic matrix slurry including a silica sol, an alumina filler, apropylene glycol processing aid, and a polyvinyl alcohol processing aidwas prepared using a conventional ball milling process. The silica solincluded colloidal silica dispersed in water. The colloidal silicaparticles constituted about 40 percent of the total weight of the silicasol, and the silica sol constituted about 28.11 percent of the totalweight of the pre-ceramic matrix slurry. The alumina filler constitutedabout 59.90 percent of the total weight of the pre-ceramic matrixslurry, and included alumina particles having an average diameter ofabout 300 nanometers. The propylene glycol processing aid constitutedabout 10.62 percent of the total weight of the pre-ceramic matrixslurry. The polyvinyl alcohol processing aid constituted about 1.37percent of the total weight of the pre-ceramic matrix slurry.

One thousand (1000) linear feet of a one inch wide tape of 1500 denierNEXTEL® 610 tows stitched together with a glass fiber was theninfiltrated with the pre-ceramic matrix slurry to form a prepreggedcomposite material on an automated prepregging device. FIG. 3A is aphotograph showing a top-down view of a portion of the tape of 1500denier NEXTEL® 610 tows prior to being infiltrated with the pre-ceramicmatrix slurry. The prepregged composite material was wound onto a reeland was provided to a conventional AFP apparatus configured to draw,place, and cut the prepregged composite material. FIG. 3B is aside-elevation view illustrating a placement head 312 of the AFPapparatus utilized, with the reel 310 of the prepregged compositematerial 302 provided thereon.

The AFP apparatus was used to form eight layers of the prepreggedcomposite material on a tool exhibiting the dimensions and shape of anaft cowl. FIG. 3C is a photograph showing a side-elevation view of theeight layers of the prepregged composite material on the tool. A firstof the eight layers was placed on a contoured surface of the tool usingthe AFP apparatus, a second of the eight layers was placed on the firstlayer using the AFP apparatus, and subsequent layers were placed in asimilar manner (e.g., a third layer was placed on the second layer usingthe AFP apparatus, a fourth layer was placed on the third layer usingthe AFP apparatus, etc.). The NEXTEL® 610 fibers of the second layerwere oriented in a direction about +45 degrees offset from that of theNEXTEL® 610 fibers of the first layer. In turn, the NEXTEL® 610 fibersof the subsequent layers (i.e., the third layer through the eighthlayer) were oriented in a direction about −45 degrees, about 90 degrees,about 90 degrees, about −45 degrees, about +45 degrees, and about 0degrees offset from that of the NEXTEL® 610 fibers of the first layer,respectively.

Following placement on the tool, the eight layers of the pre-preggedcomposite material were vacuum bagged and then cured in an autoclaveusing a maximum applied temperature of about 125° C. and a maximumapplied pressure of about 30 psi to form a cured composite materialstructure. FIG. 3D is a photograph showing a perspective view of thecured composite material structure. The cured composite materialstructure was then sintered using a maximum applied temperature of about1150° C., and subjected to conventional machining processes to form aCMC structure exhibiting the dimensions and shape of an aft cowl. FIG.3E is a photograph showing a perspective view of the resulting CMCstructure.

While the disclosure is susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, the disclosure is not intended to be limited to the particularforms disclosed. Rather, the disclosure is to cover all modifications,equivalents, and alternatives falling within the scope of the presentinvention as defined by the following appended claims and their legalequivalents.

1. A system for forming a ceramic matrix composite structure, comprising: an advanced fiber placement apparatus comprising: a placement head configured to place at least one prepregged composite material over at least one surface of a tool, the at least one prepregged composite material comprising a ceramic fiber preform infiltrated with a pre-ceramic matrix slurry; and at least one reel of the at least one prepregged composite material; a curing apparatus configured to cure the at least partially uncured composite material structure to form a substantially cured composite material structure; and a densification apparatus configured to densify the substantially cured composite material structure to form a ceramic matrix composite structure.
 2. The system of claim 1, wherein the advanced fiber placement apparatus is configured to draw, align, place, cut, and rethread the at least one prepregged composite material.
 3. The system of claim 1, wherein the advanced fiber placement apparatus is configured to place the at least one prepregged composite material over a contoured surface of a three-dimensional tool exhibiting a complex shape.
 4. The system of claim 1, wherein the advanced fiber placement apparatus is configured to manipulate at least one of the tackiness and rigidity of the at least one prepregged composite material before and during placement of the at least one prepregged composite material over the at least one surface of the tool.
 5. The system of claim 1, wherein the advanced fiber placement apparatus is configured to place multiple prepregged composite materials over the at least one surface of the tool simultaneously, sequentially, or a combination thereof.
 6. An advanced fiber placement apparatus comprising: at least one placement head configured to draw, align, place, cut, and rethread at least one prepregged composite material comprising a ceramic fiber preform infiltrated with a pre-ceramic matrix slurry; and at least one reel of the at least one prepregged composite material.
 7. The advanced fiber placement apparatus of claim 6, wherein the at least one prepregged composite material comprises: a ceramic fiber preform comprising a single tow of ceramic fibers, a tape of multiple tows of ceramic fibers, or a woven fabric of multiple tows of ceramic fibers; and pre-ceramic matrix slurry over and around the ceramic fiber preform.
 8. The advanced fiber placement apparatus of claim 6, wherein the at least one placement head is configured to cool the at least one prepregged composite material prior to placement over at least one surface of a tool and to heat the at least one prepregged composite material during placement over the at least one surface of the tool.
 9. (canceled)
 10. The advanced fiber placement apparatus of claim 6, wherein the at least one placement head is configured to increase one or more of the tackiness and the rigidity of the prepregged composite material prior to and during placement of the prepregged composite materials over the surface of the tool.
 11. The advanced fiber placement apparatus of claim 6, wherein the at least one prepregged composite material comprises an oxide-based ceramic fiber preform and an oxide-based pre-ceramic matrix slurry.
 12. The advanced fiber placement apparatus of claim 11, wherein the oxide-based ceramic fiber preform comprises one or more of alumina fibers, alumina-silica fibers, and alumina-boria-silica fibers.
 13. The advanced fiber placement apparatus of claim 12, wherein the oxide-based pre-ceramic matrix slurry comprises an oxide ceramic sol and an oxide ceramic filler.
 14. The advanced fiber placement apparatus of claim 13, wherein the oxide ceramic sol comprises one or more of alumina sol, a silica sol, and an alumina-silica sol, and wherein the oxide ceramic filler comprises particles of one or more of alumina, silica, and zirconia.
 15. The advanced fiber placement apparatus of claim 6, wherein the at least one prepregged composite material comprises a non-oxide-based ceramic fiber preform and a non-oxide-based pre-ceramic matrix slurry.
 16. The advanced fiber placement apparatus of claim 15, wherein the non-oxide-based ceramic fiber preform comprises one or more of silicon carbide fibers, silicon nitride fibers, fibers including silicon carbide on a carbon core, silicon carbide fibers containing titanium, silicon oxycarbide fibers, silicon oxycarbonitride fibers, and carbon fibers.
 17. The advanced fiber placement apparatus of claim 15, wherein the non-oxide-based pre-ceramic matrix slurry comprises a non-oxide pre-ceramic polymer and a non-oxide ceramic filler.
 18. The advanced fiber placement apparatus of claim 17, wherein the non-oxide pre-ceramic polymer is an organosilicon polymer formulated to form a non-oxide ceramic matrix through cure and pyrolysis, and wherein the non-oxide ceramic filler comprises particles of one or more of silicon carbide, silicon nitride, silicon hexaboride, aluminum nitride, boron nitride, boron carbide, titanium boride, titanium carbide, and hafnium carbide.
 19. The advanced fiber placement apparatus of claim 6, wherein the advanced fiber placement apparatus comprises multiple reels of the at least one prepregged composite material.
 20. An advanced fiber placement apparatus, comprising: reels of at least one prepregged composite material, each of the reels of prepregged composite material independently comprising at least one ceramic fiber preform infiltrated with at least one pre-ceramic matrix slurry; and a placement head configured and positioned to draw and align the at least one prepregged composite material from the reels of prepregged composite material, to place a portion of the at least one prepregged composite material over a surface of a tool, and to cut the prepregged composite material after placement of the portion of the at least one prepregged composite material over the surface of the tool.
 21. The advanced fiber placement apparatus of claim 20, wherein the placement head is further configured to heat the portion of the at least one prepregged composite material prior to placement over the surface of the tool, and to cool another portion of the at least one prepregged composite material following placement of the portion of the at least one prepregged composite material over the surface of the tool. 